KFileFilterCombo: Don't add the allTypes option if we only have 1 item
This can happen when the mime list is something like
("application/x-chm", "application/octet-stream")
so initially m_allTypes will be true because we have 2 types, but then when we process the types we see that one of them is hasAllFilesFilter and not add it to the list (we do it at the end).
Without this patch the list of mimes to chose from looks like
CHM <-- this is the all types entry
CHM <-- this is application/x-chm
All Files <-- this is application/octet-stream
With it we only have
CHM
All Files